hydrometer

/haɪˈdrɑmədər/

Other forms: hydrometers

You may have used a hydrometer in the science lab to measure the specific gravity of a liquid. Specific gravity is the density of a substance as compared to the density of water.

A hydrometer looks like a thin, transparent, closed tube, marked with a numbered scale and having a wider part at one end containing a small weight made of lead or steel. You put it into a container of the liquid whose specific gravity you're measuring, and when the surface of the liquid in the container lines up with an amount on the scale, that amount is the liquid’s specific gravity. Hydrometers are commonly used in industries that make beverages, test car batteries, and measure the salt content in aquariums. Hydrometer uses the Greek combining forms hydro-, "water," and -meter, "measure."

Definitions of hydrometer

1. noun

   an instrument for measuring the specific gravity of a liquid
   types:

   salinometer

   a hydrometer that determines the concentration of salt solutions by measuring their density

   thermogravimeter, thermohydrometer

   a hydrometer that includes a thermometer

   type of:

   measuring device, measuring instrument, measuring system

   instrument that shows the extent or amount or quantity or degree of something